Distributed spatial modulation with dynamic frequency allocation

This paper proposes a distributed implementation of spatial modulation (SM) using cognitive radios. In distributed spatial modulation (DSM), multiple relays form a virtual antenna array and assist a source to transmit its information to a destination. The source broadcasts its signal, which is independently demodulated by all the relays. Each of the relays then divides the received data in two parts: the first part is used to decide which one of the relays will be active, and the other part decides what data it will transmit to the destination. An analytical expression for symbol error probability is derived for DSM in independent and identically distributed (i.i.d.) Rayleigh fading channels. The analytical results are later compared with Monte Carlo simulations. Further, an instantaneous symbol error rate (SER) based selection combining is proposed to incorporate the direct link between the source and destination with existing DSM. Next, DSM implementation is extended to a cognitive network scenario where the source, relays, and destination are all cognitive radios. A dynamic frequency allocation scheme is proposed to improve the performance of DSM in this scenario. The frequency allocation is modeled through a bipartite graph with end-to-end SER as a weight function. The optimal frequency allocation problem is formulated as minimum weight perfect matching problem and is solved using the Hungarian method. Finally, numerical results are provided to illustrate the efficacy of the proposed scheme.     

An embedded pilot power based channel estimation and low-complexity feedback equalization scheme for OTFS system

Orthogonal Time Frequency Space modulation (OTFS) has evolved as an astounding modulation technique for high-speed communication in a doubly dispersive channel. In any wireless communication system, channel estimation and equalization are essential at the receiver to recover the transmitted data. To accomplish this for the emerging OTFS based systems, a modified embedded pilot-based channel estimation technique and low complexity feedback equalization algorithm for integer Doppler shifts in the delay-Doppler domain are proposed in this paper. Our channel estimation scheme exploits embedded-pilot arrangement, and the symbol equalization relies on the Interference calculation and its mitigation iteratively. To achieve this we contemplate a prudent arrangement of symbols in the OTFS frame in such a way that the Guard symbols prevent the interference between data symbols and the pilot symbol at the receiver. Two distinct lumps of received data of the same OTFS frame will be engaged in channel estimation and data detection. An analytical expression of the theoretical Cramer Rao Lower Bound (CRLB) is derived and plotted for the proposed channel estimation scheme. The attained simulation results for Bit-Error-Rate (BER) under the proposed scheme show a significant error rate improvement over the Minimum Mean Squared Error (MMSE) equalization algorithm. Further, a lower computational complexity is also achieved in comparison with modified MMSE detection and MP detection algorithms.     

Reduced-state maximum-likelihood detection for OFDM systems with insufficient cyclic prefix

Dispersive channels deteriorate the bit error rate (BER) performance of orthogonal frequency-division multiplexing (OFDM) systems with insufficient cyclic prefix (CP). In this paper, we first analyze the intensity of the intersymbol interference (ISI) and intercarrier interference (ICI). For performance enhancement, an effective maximum-likelihood (ML) detection method, named reduced-state maximum-likelihood (RSML), is proposed to detect all target subcarriers parallelly. For each target subcarrier, the proposed RSML detects a few nearby subcarriers jointly, while the remaining subcarriers are directly determined by using pre-detection values. Simulations results show that the proposed RSML achieves a significant performance improvement in terms of BER compared to the existing detection methods and is robust to various channel models and CP lengths. In particular, for certain channel conditions with insufficient CP, the detection performance of RSML is even better than conventional detection with sufficient CP because additional frequency diversity gain is obtained from joint detection at the expense of complexity.     

室内可见光多维CAP空间调制

针对室内可见光通信（VLC）光链路发射源（LED器件）有限的调制带宽问题,基于多维无载波幅度相位调制（CAP）技术,提出一种频带利用率高效的光空间调制方案（OSM-CAP）。OSM-CAP系统将输入信息序列分成两部分,一部分进行空域映射即空间调制,其结果用来选择激活的LED;另一部分进行信号域映射,即CAP调制。其中,CAP调制采用序列二次规划算法求取的时域正交多维CAP滤波器组实现。对于采用强度调制/直接检测（IM/DD）的VLC系统,该CAP信号还将进行单极化处理,文中提出两种相应的解决方案,即采用添加直流偏置（OSM-DCO/CAP方案）和零值位置极性编码（OSM-U/CAP方案）。基于朗伯体辐射模型,且可见光背景噪声建模为加性高斯白噪声,推导了OSM-DCO/CAP、OSM-U/CAP调制方案的误码率理论解,仿真验证了其准确性。在5 m×5 m×3 m的室内场景下,探讨了无载波幅度相位调制维度以及接收机个数、发射机间距、收发平面距离以及链路遮挡情况等信道参数对系统性能的影响。结果表明,星座调制阶数相同时,CAP调制维度越高,误码性能越好;接收机个数增多、发射机间距加大以及收发平面距离减小与系统可靠性存在正相关关系;链路存在遮挡情况时,会提高信道间的差异性,改善系统性能。     

基于幅度相位联合校正算法的8-QAM自由空间相干光通信

提出了基于幅度相位联合校正算法的8阶正交幅度调制(8-QAM)自由空间相干光通信方案。与传统的自由空间光通信方案相比,本文提出的方案不仅无需信道状态信息(CSI)就可以实现对原信号的高精度还原,同时还具有较高的光谱效率。仿真实验表明,当接收端与发射端的频偏f₀=20 MHz、激光器联合线宽Δf=10 kHz、信噪比为20 dB时,该方案在归一化大气闪烁标准差σ=0.25、归一化相位噪声方差σ■=0.07的对数正态湍流信道条件下,其误码率(BER)与未采用联合校正算法的8-QAM系统相比低4个量级。     

Analysis of physical layer performance of data center with optical wavelength switches based on advanced modulation formats

In this paper the IRIS (Integrated Router Interconnected spectrally), an optical domain architecture for datacenter network is analyzed. The IRIS integrated with advanced modulation formats (M-QAM) and coherent optical receiver is analyzed. The channel impairments are compensated using the DSP algorithms following the coherent receiver. The proposed scheme allows N2 multiplexed wavelengths for N×N size. The performance of the N×N-IRIS switch with and without wavelength conversion is analyzed for different Baud rates over M-QAM modulation formats. The performance of the system is analyzed in terms of bit error rate (BER) vs OSNR curves.     

Deep neural network-based detection of index modulated MIMO-OFDM

Multiple-input multiple-output orthogonal frequency division multiplexing with index modulation (MIMO-OFDM-IM) has been introduced as a new transmission method for 5G and beyond communications. On the other hand, deep neural networks (DNNs) have started to be effective in many fields, including wireless communication, due to their advantages such as low complexity, high performance, low processing times, etc. Since the optimum decoding for MIMO-OFDM-IM grows exponentially with higher modulation orders and the number of transmit and receive antennas, DNN-based decoding will be a potential choice for the next generation receiver architecture. In this work, a novel fully connected DNN based MIMO-OFDM-IM to jointly detect the transmitted symbols from each antenna is proposed and its performance is analyzed. As seen from the simulation results, the proposed DNN-based detector shows a close bit error rate performance to optimum detection with lower computational complexity.     

SER estimation method for 56 GBaud PAM-4 transmission system

In this Letter, we have proposed a generalized Gaussian probability density function(GGPDF)-based method to estimate the symbol error ratio(SER) for pulse amplitude modulation(PAM-4) in an intensity modulation/direct detection(IM/DD) system. Furthermore, a closed form expression of SERGGDfor PAM-4 has been derived. The performance of the proposed method is evaluated through simulation as well as experimental work.The fitting of probability density functions of the received signal is applied via GGPDF and shape parameters P1 and P2 associated with different PAM-4 levels are determined. The optimum single value of shape parameter P is then calculated to estimate the SER. The mathematical relationship of P with different received optical powers and receiver bandwidths has been determined and verified. The proposed method is a fast and accurate method to estimate SER of a PAM-4 system, which is more reliable and in agreement with the error counting method.     

一种面向中继协作频谱感知系统的自适应全局最优化算法

该文研究了冗余中继, 次用户及中继用户数目, 检测门限, 信道传输错误率等因素对中继协作频谱感知系统性能的影响, 并提出一种新的自适应全局最优化算法.该算法基于获得最大无干扰功率的自适应中继选择方法, 确定备选认知中继集合;单个次用户以信道传输错误率最小为准则, 从备选认知中继集合中自适应选择最佳中继, 使总体检测率最大;在给定目标检测率的条件下, 以系统吞吐量最大为准则, 给出了自适应全局最优化算法.仿真实验结果表明新算法信道传输精度高, 信道吞吐量大, 节约带宽资源.     

Gamma-Gamma湍流信道中大气光通信系统误码特性分析

大气信道中的大气湍流是影响无线激光通信系统性能的主要因素之一, 其引起的强度闪烁效应会对接收信号的提取和还原造成很大干扰。基于Gamma-Gamma概率分布的大气湍流信道统计模型, 研究了利用副载波相移键控(PSK)强度调制技术的大气光通信系统的误码特性; 推导了副载波二进制相移键控(BPSK)及开关键控(OOK)两种调制模式下的系统误码率表达式; 对在一定条件下的大气光通信系统, 比较了副载波BPSK和OOK两种调制模式的误码特性; 分析了链路特征、接收口径尺寸、通信波长和天顶角等因素对系统误码率的影响。结果表明, 增大接收孔径和通信波长都能有效地降低系统误码率, 而天顶角的增大则会使系统误码率增加, 副载波BPSK调制模式的误码特性要优于OOK调制模式的误码特性。     

室内可见光无载波幅度相位调制系统性能分析

针对室内可见光通信调制技术问题,提出翻转光无载波幅度相位调制和单极性光无载波幅度相位调制两种功率有效的调制方案,二者分别采用"正、负模块极性分组"以及"零值位置极性编码"方法实现信号单极性处理,以满足可见光通信"强度调制/直接检测"的要求.基于朗伯辐射模型,考虑到高斯背景光噪声的可见光直射传输信道,推导了包括直流偏置光无载波幅度相位调制在内的三种调制方案的误比特率闭式表达式,仿真验证了其准确性.在此基础上,分析比较了三者频带利用率,讨论了信道参量对光无载波幅度相位调制系统误码性能的影响,结果表明,在5m×5m×3m的室内场景下,与发射机辐射角为30°和45°相比,0°时的系统误码性能分别优于6.9dB和29.9dB;收发机距离为1m时,误码性能比2m时改善近12dB.     

Relay selection and nonlinear energy harvesting in full-duplex multi-relay cooperative network

Energy harvesting (EH) is a promising technique to extend the lifetime energy-constrained devices in wireless networks. This paper analyses the significance of relay selection and non-linear EH in evaluating the performance of Full-duplex (FD) decode-and-forward (DF) multi-relay cooperative network. The relay selection is considered under three scenarios based on channel state information (CSI) availability. We compare the EH performance of a hybrid power-time-splitting (PTS)-based non-linear energy harvester with time-spitting (TS) and power-splitting (PS) EH at the relay node. We derive the expression of outage probability (OP) of FD DF multi-relay cooperative network over independent and identically distributed Rayleigh fading channels. Numerical results show that the outage performance of the system is significantly enhanced by deploying an ideal relay selection scheme. This paper also gives insights about the combined effect of saturation threshold of non-linear EH and residual self-interference (RSI) on the system performance. Unlike linear EH systems, the non-linear EH causes the outage floor even when the RSI is significantly small. The response of the system is also analysed for the impact of TS and PS ratios. Furthermore, we also investigate the system’s performance in terms of other system parameters like the number of relays and data transfer rate. Monte Carlo simulations are used to verify the analytical expressions.     

Receiver structure and estimation of the modulation index for tamed frequency modulated (TFM) signals

Tamed frequency modulation (TFM) is a spectrally efficient constant amplitude continuous phase modulation (CPM) scheme which can be simply realized by using a frequency modulator (FM). In the implementation the modulation index of TFM is calibrated to have a nominal value of 0.5, but due to temperature variations it can drift causing time varying phase jitter. In this paper we present novel algorithms and performance results to measure and control the modulation index in a coherent receiver based on the joint reduced state sequence detector (RSSD) and per-survivor processing (PSP) carrier phase estimation. The modulation index estimator measures phase transitions in the receiver and derives estimates by comparing the result to the coding rule of the TFM signal. The estimator has acquisition and tracking ability, and the current estimate can be used to replace the nominal index value. Our simulation results show that the proposed coherent receiver with the novel modulation index estimator has less than 1 dB performance degradation compared to around 4.5 dB exploiting only the PSP carrier phase estimation.     

Model and comparative analysis of reduced-complexity receiver designs for the LTE-advanced SC-FDMA uplink

Due to its favorable peak-to-average power ratio (PAPR), a single-carrier frequency-division multiple access (SC-FDMA) scheme has been chosen for the 3GPP Long Term Evolution Advanced (LTE-A) uplink, as opposed to the orthogonal frequency-division multiple access (OFDMA) scheme used in the downlink. SC-FDMA, however, is prone to suffer from the effects of inter-symbol interference. When combined with multiple-input multiple-output (MIMO) transmission, the complexity of optimal detection for SC-FDMA grows exponentially with the product of the number of transmitting antennas and the channel length. A means to reduce the complexity is to equalize the channel in the frequency domain first, similar to OFDMA, followed by detection in the time domain, using well-developed standard receivers for flat fading MIMO channels. Apparently, these reduced-complexity two-stage receivers suffer from a rate loss as a consequence of their simplifying design assumptions. In this paper, we provide an extensive model of SC-FDMA transmission with frequency domain equalization (FDE). Based on this model, we derive the achievable rates of four reduced-complexity two-stage receivers within the mismatched receiver framework in terms of generalized mutual information (GMI). The rate expressions allow us to assess the rate loss as compared to the optimal receiver for varying channel parameters such as channel length and spatial correlation. It is shown, for instance, that a distributed subcarrier mapping which is beneficial from a frequency diversity point of view substantially deteriorates the achievable rates. It is also explained how this loss can be compensated for by combining time-domain detection with frequency-domain interference cancelation.     

Decode-and-forward with quadrature spatial modulation in the presence of imperfect channel estimation

The performance of quadrature spatial modulation (QSM) multiple-input multiple-output (MIMO) system with cooperative decode and forward (DF) relays is analyzed in this paper. QSM is a new MIMO transmission technique that enhances the overall performance of conventional spatial modulation through exploiting quadrature spatial dimension. A practical scenario is considered where the channel is estimated at the relays and the destination and the impact of channel estimation error is investigated. Two cooperative systems are considered in the study. In the first system, multiple single-antenna DF relays are assumed, whereas, in the second system, single multiple-antennas DF relay is considered. For both systems, an analytical expression for the pair wise error probability (PEP) is obtained. As well, an asymptotic expression for the PEP at high and pragmatic signal to noise ratio is derived. Derived expressions are used to provide an upper bound on the average bit error ratio. The derived analysis is corroborated through Monte Carlo simulations and results demonstrate a close-match for a wide range of SNR values.     

相干光脉冲位置调制信道容量及传信率最大化研究

分析了相干光脉冲位置调制的信道容量及传信率最大化条件.通过分析光外差接收的脉冲位置调制信号具有的概率分布特性,推导出采用最大似然检测的相干脉冲位置调制信道具有的转移概率矩阵和信道容量,证明在检测器散粒噪声极限假设下,信道容量只取决于接收脉冲能量和脉冲位置调制阶数.利用Jensen不等式化简信道容量得到其下限,该下限能够近似实际通信链路的信道容量.基于此估计出达到最高传信率时的脉冲位置调制阶数同粒子数反转的重建时间之间的关系,给出了二者在一定范围内的一般映射.数值仿真表明,在接收能量使信道误码率优于10-2时,估箅出的脉冲位置调制阶数能够使传信率接近最大值.     

Cooperative communication with imperfect channel information: Performance analysis and optimum power allocation

In this paper, symbol-error-rate (SER) performance analysis is provided for decode-and-forward (DF) and amplify-and-forward (AF) cooperation schemes in wireless networks with imperfect channel information. We derive closed-form SER formulations for a single relay system with square MQAM signals in a flat Rayleigh fading channel. Moreover, closed-form and high SNR tight SER approximations are established to show the asymptotic performance of the cooperation protocols. Simulations and comparisons verify that these approximations lead to similar results to those from the exact SER formulations for different power allocation methods. Furthermore, based on these SER performance analyses, we determine the optimum power allocation for the AF and DF cooperation scenarios.     

A method for the construction of hierarchical generalized space shift keying (GSSK) modulation for unequal error protection

In this paper, we propose a systematic method to achieve two-level unequal error protection (UEP) with generalized space shift keying (GSSK) modulation for multiple-input multiple-output (MIMO) systems. GSSK is a modulation scheme that encodes the source information in the antenna indices. To enable the nonuniform arrangement of the spatial constellation of GSSK modulation, new techniques are needed as new features of GSSK modulation are observed. The proposed method is based on first partitioning the GSSK constellation into subsets and then choosing constellation points inside a subset. The high-priority (HP) bits select the subset and the low-priority (LP) bits select constellation points inside a subset. The proposed subset partitioning procedure developed based on a theoretical study on set partitioning in the multidimensional space guarantees optimal or near-optimal HP protection, enables simple and systematic designs for LP protection, and increases the LP capacity. The proposed systematic design approach applies to systems with any numbers of transmit antennas and can create various hierarchical GSSK schemes with different HP/LP protection capabilities.     

Deep-BiGRU based channel estimation scheme for MIMO–FBMC systems

Deep Learning (DL)–based wireless communication systems have the potential to improve the conventional functions and current architecture of communication systems. In this paper, we propose a novel DL-based channel estimation scheme for multiple-input multiple-output filter bank multicarrier with offset quadrature amplitude modulation (MIMO-FBMC/OQAM) systems called deep bidirectional gated-recurrent unit (BiGRU) scheme. This scheme can easily be applied to a single-input single-output (SISO) system. The proposed scheme is divided into two stages: offline and online. The network is first trained in the offline stage. The prediction of channel information and estimation of the channel matrix using the trained network is then performed in the online stage. The simulation results in terms of the normalized mean square error (NMSE) and bit error rate (BER) demonstrate that, under different time-varying channel models, the proposed DL scheme significantly improves the channel estimation performance of FBMC for single and multiple antennas compared to conventional interference approximation method (IAM) channel estimation methods.